A number of antenna designs and systems exist within various industries for enabling operation of a single antenna at several frequency bands for multiple applications. The antenna system configuration is the key factor that determines the number and location of such frequency bands. In general, a multiband antenna experiences a frequency detuning or offset when operating under conditions subject to the presence of extraneous materials that may electromagnetically couple to the antenna. Both electrically conductive and dielectric materials may significantly detune the antenna to render it inoperative at certain frequencies of interest.
This situation becomes more critical for antenna applications used in portable and handheld electronic devices, which may be affected by the presence of any combination of user body parts (e.g., hands, fingers, head or other parts of the body as when such device is placed in a pocket or hung on clothing), conductive materials, or dielectric materials located within a radius of two wavelengths at the lowest frequency of operation in the medium where the antenna element is operating. As a result, in certain applications, a multiband antenna designed for the specific frequency bands of the intended applications cannot be used.
In recent years, the demand for multiband antennas has increasingly grown for applications in the touchscreen, mobile platform, and automobile industries. In particular, the implementation of multiband antennas have been addressed in the prior art, as described in U.S. Pat. No. 8,749,438 to Jenwatanawet et al., the specification of which is incorporated herein by reference in its entirety. However, these efforts have faced certain challenges and limitations. Particularly, attempts made to provide robust single-antenna designs to withstand antenna detuning and at the same time capable of effectively and efficiently complying with signal integrity standards set up by industry have not been successful. A major challenge is that antennas are susceptible to being detuned by the presence of extraneous materials unless the antenna is enclosed in a separate module, making it bigger and more expensive. Likewise, multiple antenna elements are used to be able to operate at different frequency bands, which make the size requirements significantly larger and the need to use a larger number of or more complex electronic components.
As a result, a compromise is required between two conflicting goals. Firstly, making the antenna system robust enough to prevent detuning, which typically involves an antenna with wider frequency bandwidth than the minimum required; and secondly, making the antenna less susceptible to undesired noise, signal interference, or electromagnetic coupling effects that may affect or be induced by the antenna element, which means using an antenna with as minimum frequency bandwidth as possible.
Alternatively, an antenna design having a frequency band of operation that is larger than the required bandwidth that includes the different frequency bands of the intended applications may overcome frequency detuning. In other words, a wideband antenna that is detuned may still operate at the frequencies of interest. However, this requires the antenna to operate at frequencies of no operational interest, which may result in undesired noise, signal interference, or electromagnetic coupling effects that may affect or be induced by the antenna element.
Accordingly, manufacturers intending to use antennas for multiple applications in significantly constrained operational conditions experience either an unacceptable system sensitivity to detuning or an unacceptable system performance that does not meet signal integrity requirements. This leads manufacturers to implementation of antenna systems that are costly, aesthetically unappealing, or more importantly, highly inefficient by using adaptively tuned antenna elements, multiple antenna elements in a diversity configuration, or automatic mechanisms to increase the power transmitted by the antenna system.
Previous efforts have been made to develop wideband antenna elements for multiple applications, as described in U.S. Pat. No. 8,766,856 to Hsieh, et al., the specification of which is incorporated herein by reference in its entirety. However, these efforts typically result in using an antenna operating at significant frequency ranges of no operational interest for the intended applications. This faces severe challenges and limitations. While the approach of using a wideband antenna is effective in reducing or preventing significant antenna detuning, a major limitation may result where the system receives spurious signals from other sources that increase the noise level of the system. Another limitation may result where the antenna system radiates spurious signals that may interfere with other internal and external electronic systems. These limitations may compromise the signal integrity of internal and/or external systems or make it very challenging for a wideband antenna to meet signal integrity industry standards. As a result, this approach is not able to effectively prevent antenna detuning under operational conditions. Thus, even though the robustness of the antenna is improved, the signal integrity limitations may result in an overall antenna system performance that is unacceptable to meet industry standards.
A way to address the disadvantages of the efforts attempted by the prior art is to design a desensitized antenna system that integrates a desensitizer element with an antenna element. This would make it possible to increase the robustness of the overall antenna system while mitigating or eliminating undesired effects, by configuring the desensitizer element to constrain the operation of the antenna system at frequencies of no operational interest. In particular, a configuration may be designed to integrate an antenna and desensitizer element with a feeding mechanism and the corresponding transmission line in a single unit for additional advantages.
Currently, there is no well-established method of deterministically creating a desensitized antenna system that adapts to the frequency bands of operation, prevents undesired transmission and reception at frequencies of no operational interest, and effectively withstands frequency detuning under operational conditions.
Thus, there remains a need in the art for antenna systems and methods to desensitize antennas that are capable of a robust operation at the frequencies of intended applications, while avoiding the problems of prior art systems and methods.